Term
| What are the basics of the somatic nervous system? |
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Definition
Somatic nervous system: The portion that acts upon the body’s external environment, primarily through the actions of skeletal muscles.
1.This utilizes mostly voluntary responses to consciously perceived sensory signals.
2.Functional designations: General somatic motor system and Special visceral motor system. These designations reflect the fact that skeletal muscles develop from two different embryonic sources: myotomes (a general somatic source) and the walls of the pharynx (a special visceral source).
3.Functional components of neurons: General somatic efferent (GSE) and Special Visceral Efferent (SVE) |
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Term
| What are the basics of the ANS? |
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Definition
Autonomic nervous system(ANS): The portion that acts upon the body's internal environment, primarily through the actions of viscera (i.e., cardiac muscle, smooth muscle, glands) (By definition, the ANS is a pure motor pathway)
1.This utilizes mostly involuntary responses to sensory signals not consciously perceived.
2.Functional designation: General visceral motor system.
3.Functional component of neurons: General Visceral Efferent (GVE). |
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Term
| What is the basic structure of the somatic nervous system? |
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Definition
The peripheral part of the somatic nervous system (to skeletal muscle) is a one-neuron system:
a)Cell bodies are located within the CNS.
b)In the brain, cell bodies are located in brainstem motor nuclei. In the spinal cord, cell bodies are located in the ventral horn of gray matter.
-The motor neurons will innervate skeletal muscle. The somatic pathway will send its axons to the ending called the motor end plate
-Contains Dorsal root ganglia (has pseudounipolar neurons)
c)Axons leave the CNS through cranial nerves, or, ventral roots of spinal nerves.
d)Axons run the entire distance to the target muscles through peripheral nerves, without intervening synapses |
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Term
| What are the characteristics of neuron #1 in the ANS's 2-neuron system? |
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Definition
Neuron #1 = preganglionic neuron = presynaptic neuron.
1)Cell bodies are located within the CNS.
2)In the brainstem, cell bodies are located in specific autonomic nuclei. In the spinal cord, cell bodies are located in the lateral (=intermediolateral) horn of gray matter.
3)Axons leave the CNS through certain (not all) cranial nerves, or, through certain (not all) ventral roots of spinal nerves;
4)Axons generally DO NOT innervate the target viscera. Instead, they synapse with second autonomic neurons, which in turn innervate the target viscera. |
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Term
| What are the characteristics of neuron #2 in the ANS's two-neuron system? |
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Definition
Neuron #2 = postganglionic neuron = postsynaptic neuron.
1)Cell bodies are located outside the CNS, within autonomic (= visceral) ganglia.
2)Axons innervate the target viscera.
3)Postganglionic runs out to the target organ, but there is no motor end plate as w/ skeletal muscle
4)Cell bodies will be multipolar
i.Dorsal root ganglia known as sensory ganglia
ii.Autonomic ganglia have synapse of pre/post ganglionic neurons
They are never the same thing |
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Term
| What are the characteristics of the sympathetic division of the ANS? |
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Definition
1.Cell bodies of preganglionic neurons are located in the spinal cord (lateral horn), from levels Tl-L2/3.
2.Axons of preganglionic neurons leave the CNS through ventral rootlets/roots and spinal nerves, from levels Tl-L2/3.
3.Preganglionic axons run from thoracolumbar levels of the spinal cord to ganglia located near the vertebral column, where synapses usually occur with postganglionic neurons.
4.Cell bodies of postganglionic neurons usually are located in ganglia near the vertebral column. These are termed paravertebral or prevertebral ganglia, according to their specific locations.
a)If located along sides of verterbral column -> paravertabral ganglia
1)Also physically associated with anterior side of aorta, therefore referred to as pre-aortic ganglia
b)If located along anterior side (front of bodies of verterbrae) --> prevertbral ganglia
5.Preganglionic axons are relatively short. Postganglionic axons are relatively long. |
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Term
| What are the neurotransmitters used in the sympathetic division? |
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Definition
a)Preganglionic neurons utilize acetylcholine at synapses with postganglionic neurons.
b)Postganglionic neurons usually utilize noradrenalin/norepinephrine at synapses with target structures.
c)Sympathetic division often is referred to as a noradrenergic system.
Exception: Sweat glands are sympathetic so the postganglionic neuron will be ACh.
d)Remember: The somatic motor system utilizes acetylcholine at the neuromuscular junction.
Function primarily in emergencies, preparing individuals for fight or flight and thus increase heart rate, inhibit GI motility and secretion, and dilate pupils & bronchial lumen. |
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Term
| What are the characteristics of the parasympathetic division? |
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Definition
Parasympathetic division (= craniosacral outflow).
1.Cell bodies of preganglionic neurons are located in the:
a)Brainstem
b)Spinal cord (lateral horn), from levels S2-4.
2.Axons of preganglionic neurons leave the CNS through:
a)Cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), X (vagus).
1)Vagus carries a large parasympathetic outflow below the head
b)Ventral rootlets/roots and spinal nerves, from levels S2,3,4.
1)(S2, 3, 4 keeps the penis off the floor)
3.Preganglionic axons run from craniosacral levels of the CNS to ganglia located within or very close to the target structures, where synapses occur with postganglionic neurons.
4.Cell bodies of postganglionic neurons are located in ganglia within or very close to the target structures. In the head, these are cranial parasympathetic ganglia. Below the head, these are termed terminal (= intramural = intrinsic) ganglia.
a)Postganglionic neurons are distributed to the walls of the visceral organs and glands of the digestive system but not to the skin or to the periphery
5.Preganglionic axons are relatively long. Postganglionic axons are relatively short.
a)Preganglionic neurons travel a long distance and synapse very close to target organ |
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Term
| What are the neurotransmitters used by the parasympathetic division? |
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Definition
a)Both pre- and postganglionic neurons utilize acetylcholine at their synapses.
b)Parasympathetic division is often referred to as a cholinergic system.
Decrease heart rate, increase GI peristalsis, & stimulate secretory activity
Function primarily in homeostasis, tending to promote quiet and orderly processes of the body. |
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Term
| What is the general function of the sympathetic division? |
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Definition
1.Sympathetic activity is more widespread and indirect. The ratio of pre- to postganglionic neurons is 1:15 or more.
2.Innervates cardiac and smooth muscle and glands in all areas of the body.
a)Sympathetics go everywhere
3.Functions are associated with increased levels of activity or excitation, and assistance in coping with stress and physical exertion. This is the classic "fight, fright, or flight" response. |
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Term
| What is the general function of the parasympathetic division? |
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Definition
1.Parasympathetic activity is more specific and direct. The ratio of pre- to postganglionic neurons is 1:2.
2.Does not innervate the body wall or limbs.
a)They will be in the head and genitalia
3.Functions are associated with homeostasis, restoration, recuperation, and relaxation. This is the classic "vegetative state" response. |
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Term
| How do sympathetic and parasympathetic divisions work together? |
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Definition
The sympathetic and parasympathetic divisions often function as antagonistic systems (e.g., sympathetics producing cardiac acceleration vs. parasympathetics producing cardiac deceleration). HOWEVER there are always exceptions,
1.The two divisions may function as complementary (= synergistic) systems (e.g., Parasympathetics producing erection and sympathetics producing ejaculation in normal sexual function).
a)Point and Shoot (or Skeet)
2.One division may function as an independent system (e.g., Sympathetics activate sweat gland secretion. The parasympathetics play no role in sweat gland activity)
a)They are turned off when the sympathetics cease their firing. If there is no sympathetic stimulation, then they will not secrete (no antagonistic response) |
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Term
| What are the sympathetic pathways? |
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Definition
The sympathetic division innervates all parts of the body. However, there are 4 general pathways to 4 specific target regions:
1.Spinal nerves ----> Body wall and limbs.
2.Carotid artery hitch-hikers ----> Head and upper neck.
3.Cervicothoracic nerves ----> Viscera in thoracic cavity.
4.Splanchnic nerves ----> Viscera in abdominopelvic cavity + external genitalia |
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Term
| What are the parasympathetic pathways? |
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Definition
Compared with the sympathetic division, the parasympathetic division is much more limited in scope and much less complex in its pathways
The parasympathetic system is focused on glands and smooth muscle in the head, and on the cardiovascular, respiratory, digestive, and urogenital viscera. There is no parasympathetic innervation to the body wall or limbs. |
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Term
| How do sympathetic neurons get to their target of the body wall and limbs? |
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Definition
1. Axons of preganglionic neurons leave the CNS through ventral roots and spinal nerves at levels T1-L2/3.
2.Preganglionic axons leave each spinal nerve, and pass through a white ramus communicans to enter a sympathetic chain ganglion.
3.Preganglionic axons synapse with postganglionic neurons within the paravertebral ganglia
4.Axons of postganglionic neurons leave the paravertebral ganglia at the ganglionic level at which they originate
-Postganglionic axons pass through a gray ramus communicans to enter a spinal nerve.
5.Postganglionic axons distribute to the body wall and limbs by traveling through spinal nerves and their branches |
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Term
| What are white rami communicans? |
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Definition
White rami communicantes connect spinal nerves T1-L2/3 with sympathetic ganglia at their own segmental levels
White rami communicantes contain preganglionic sympathetic GVE fibers with cell bodies located in the lateral horn of the spinal cord and GVA fibers with cell bodies located in the dorsal root ganglia
White rami are so named because the contained preganglionic axons are larger (relative to postganglionic axons), typically myelinated, and have a relatively shiny white appearance in life. |
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Term
| What is the structure of the sympathetic ganglia? |
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Definition
The sympathetic ganglia are linked together in a segmental, chain-like arrangement along each side of the vertebral column, thus forming a pair of "sympathetic chains."
Because of their location, the chain ganglia collectively are termed "paravertebral ganglia."
The sympathetic chains extend above and below the Tl-L2/3 levels, along the entire length of the vertebral column and sacrum.
a)Typically, there are only 3 cervical chain ganglia (superior, middle, inferior), formed by fusions of segmental embryonic ganglia.
b)Lumbar and sacral ganglia are highly variable in form and number. Fusions of ganglia are common.
c)A single, midline coccygeal ganglion (= ganglion impar), representing a fusion of the embryonic paired ganglia, is the caudal end of the sympathetic chains |
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Term
| Preganglionic axons synapse with postganglionic neurons within the paravertebral ganglia in one of which three locations? |
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Definition
1.At their own segmental level, or,
2.At a higher segmental level (in cervical sympathetic chain ganglia), after ascending through the chain, or,
3.At a lower segmental level (in lower lumbar or sacrococcygeal chain ganglia), after descending through the chain. |
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Term
| What are gray rami communicans? |
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Definition
1.Postganglionic axons pass through a gray ramus communicans to enter a spinal nerve.
a)Gray rami communicantes connect sympathetic chain ganglia with the spinal nerves at their own segmental levels (cervical and atypical lumbosacral ganglia are something of an exception).
1) Have cell bodies located in the sympathetic trunk
b)Gray rami are so named because the postganglionic axons are smaller (relative to preganglionic axons), typically unmyelinated, and have a relatively dull appearance in life
c)Remember: There is a gray ramus communicans for each spinal nerve. |
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Term
| What structures do sympathetic neurons innervate in the body wall and limbs? |
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Definition
Skeletal muscle, erector pili muscle (smooth muscle), vascular smooth muscle (blood vessels)
-This allows control of vessels, and sweat glands |
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